“What’s gonna happen when president Cruz declares gay marriage illegal by executive order?”
He will not. There is 0 pressure from conservative electorate to have this reversed. If tomorrow the SC legalized gay marriage across US, the decision would be met by a collective shrug, just look at Utah. If the people do not rise up, don’t expect a politician to risk his career to save the nation in the face of collective apathy.
I think that's why they went for the reddest state. If Utah does not care, America as a whole certainly does not care. People don't want to believe it, but it's true: the country many of us knew and loved is OVER.